1. Field of the Invention
The present invention relates to a method of forming a patterned mask layer, and more particularly, to a method of forming a patterned mask layer by a multiple patterning approach.
2. Description of the Prior Art
The development of semiconductor integrated circuit technology progresses continuously and circuit designs in products of the new generation become smaller and more complicated than those of the former generation. The amount and the density of the functional devices in each chip region are increased constantly according to the requirements of innovated products, and the size of each device has to become smaller accordingly. However, photolithography technology is used to form patterned structures in general semiconductor manufacturing processes. The size and the spacing between the patterned structures are limited by the exposure resolution minimum of the photolithography technology and hard to be further shrunk, and that becomes a bottleneck issue of the semiconductor technology. The sidewall image transfer (SIT) technology has be provided by the related industries for transferring patterns of the sidewall with size smaller than the exposure resolution minimum of the photolithography technology.
Please refer to FIGS. 1-3. FIGS. 1-3 are schematic drawings illustrating a conventional method of patterning a mask layer. As shown in FIGS. 1-3, sidewall spacers 92S are used as a mask for patterning a mask layer 90, and the patterned mask layer may be used to form patterned structures such as trenches and fin structures. As shown in FIG. 1 and FIG. 2, the sidewall spacers 92 are formed by performing an etching back process to a spacer material layer 92 conformally formed on the mask layer 90 and mandrels 91 on the mask layer 90. The sidewall spacer 92 has a taper part 92F especially when the distance between two adjacent mandrels is extremely small. As shown in FIG. 2 and FIG. 3, the mandrels 91 are removed after the step of forming the sidewall spacers 92S, and apart of the mask layer 90, which is not covered by the sidewall spacers 92S and the mandrels 91, will be damaged by an etching process for removing the mandrels 91 because of the taper parts 92F of the sidewall spacers 92S. Therefore, the shape of the patterned mask layer formed by etching the mask layer 90 with the sidewall spacers 92S as a mask will not be uniform, and uniformity of the critical dimension and/or the depth of patterned formed by using the patterned mask layer as a mask will be affected accordingly.